Just curious what is different. I did some work on it tonight hoping to get it to have spark, but no dice. Wiring has been played with, it has a pushbutton for a starter switch, and a push pull switch for the kill (I assume).

No the switch is different. It's a 3 position switch. off-run-start
No connection in run
1 terminal to ground in off, kills ignition.
other terminal to ground in start, turns on starter solenoid to crank engine.

I discovered low voltage in the power wire to the coil today. Further isolating the circuit also showed a short to ground in the wire to the coil. Pulled the flywheel cover and found something odd. ATOM computer ignition, Sydney Australia. The coil power wire insulation was chewed through by mice so I ran a test wire which still showed a short to ground. Further tests showed that the coil primary winding has only 0.9 ohms resistance to ground, it has direct battery power which I'm thinking is incorrect. I think this may be a conversion gone bad, power was running straight to the coil, the blue wire of the "ignition module" was tied in there. I don't see how the coil primary would have toggled to induce voltage in the secondary winding when the field collapsed. Somebody who knows about these ATOM modules would be helpful, I'm thinking it isn't wired correctly.

Anybody know what the primary resistance of the coil should be? The service manual is a little skecthy but appears to show 400 ohms is more like it. FWIW the points are still on the engine and they appear to open and close fine.

You have magneto ignition, no battery power used, to shut ignition off, ground the coil.My manual doesn't give any ohm readings for magneto's only 400ohms for SSI units, we probably have the same manual.Try to see if you can get spark without grounding the coil and no battery voltage any where.

Happened to have the donor HH100 on the lower shelf. Went back out & took a picture. The points (under the cover on the left) wire runs to an insulated plastic screw point & connects there with both the coil wire (shown ) and the Switch Ground (still on the tractor). Looks like all you're missing is the condensor & some wire?

Wish that picture was a little larger but it works. Looks like I need to round up a condenser somewhere and an ignition switch. I looked at switches in the TSC (tractor supply company) tonight, one looked close but no specifics on the package. It only had 2 terminals on the back but used the same style key.

Tomorrow I'll have to fiddle with that stuff and get the variable lever lock button freed up so I can have Park.

I tried everything yesterday and it appears there is just no spark coming from the old mag. It is shot. I think I am going to switch over to a standard points ignition setup. I already have a good GM coil so I'll need to pick up a condenser and I think there is a ballast resistor at my dads place. A little rewiring will be needed but I think this will be the best and most cost effective solution. It will still look right to the untrained eye. Plus it will offer more cost effective repair cost down the road.